viirya commented on issue #24557: [SPARK-27653][SQL] Add max_by() SQL aggregate function URL: https://github.com/apache/spark/pull/24557#issuecomment-490956031 I've checked few test cases regarding null values in Presto: ``` presto> select max_by(x, y) from ( values ('a', null), ('b', null), ('c', null) ) as t (x, y); _col0 ------- NULL (1 row) Query 20190509_050643_00001_ww5mk, FINISHED, 1 node Splits: 1 total, 1 done (100.00%) 0:02 [0 rows, 0B] [0 rows/s, 0B/s] presto> select max_by(x, y) from ( values ('a', null), ('b', null), ('c', 10) ) as t (x, y); _col0 ------- c (1 row) Query 20190509_050655_00002_ww5mk, FINISHED, 1 node Splits: 1 total, 1 done (100.00%) 0:00 [0 rows, 0B] [0 rows/s, 0B/s] ``` The results match the added test cases here. About prestodb/presto#2040, it is happened by null reference for the key field in Presto. This shouldn't be in our case.
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